The FBI used mob muscle to solve the 1964 disappearance of three civil rights volunteers in Mississippi, a gangster's ex-girlfriend testified Monday, becoming the first witness to repeat in open court a story that has been underworld lore for years.

Linda Schiro said that her boyfriend, Mafia tough guy Gregory Scarpa Sr., was recruited by the FBI to help find the volunteers' bodies. She said Scarpa later told her he put a gun in a Ku Klux Klansman's mouth and forced him to reveal the whereabouts of the victims.

The FBI has never acknowledged that Scarpa, nicknamed "The Grim Reaper," was involved in the case. The bureau did not immediately return a call for comment Monday.

Schiro took the stand as a witness for the prosecution at the trial of former FBI agent R. Lindley DeVecchio, who is charged in state court with four counts of murder in what authorities have called one of the worst law enforcement corruption cases in U.S. history.